Monday, August 8, 2011

A Convergence of Wonders, Day 16: Our Home Mountains, Giant Swimming Reptiles, and a Bunny

After 15 days and 4,200 miles, we woke up to the last day of our Convergence of Wonders, the geological tour of the Pacific Northwest and Northern Rocky Mountains. It was June 30th. We had traveled through the Cascades and the Coast Ranges, the present-day manifestation of convergence along the Cascadia Subduction Zone. We had traveled across the Columbia Plateau and the Channeled Scablands, and looked at evidence of past convergence in Montana's Glacier National Park, and Sun Canyon. We explored the inner parts of the earth's crust along the Beartooth Highway, and saw the evidence for a gigantic mantle plume (hot spot) at Yellowstone National Park. We saw the vast heavings of fault lines in the crust at Grand Teton National Park. And now, after a series of adventures in Utah and Nevada, we were finally headed home.

In the most technical sense, we could have started driving and made it home for a late lunch. But we couldn't pass up several of the most spectacular geological sights of our trip. We were almost home, but we could still be distracted by geological sights!

When we arrived at Berlin-Ichthyosaur State Park very late the previous night, not a few of our students were just a bit spooked by finding we were spending the night in a ghost town. The menacing looking ruins of the dark night were a little less nerve-wracking in the morning sun, so we packed and headed up to the quarry for a tour. Berlin-Ichthyosaur is a two-fer park: it preserves a late 1800's gold mining town, and a 200 million year old paleontology dig.
The ichthyosaurs were the dolphins/whales of the dinosaur era, the Mesozoic, aside for being in the wrong biological class. Whales and dolphins are mammals, of course, and the mammals were a rather minor part of the Mesozoic ecosystem, and as far as I know, none of them were adapted to marine conditions. Ichthyosaurs were air-breathing reptiles that were wonderfully adapted to life in the sea. They had the four limbs of their terrestrial ancestors, but their body shape was streamlined for fast swimming in the oceans. There were many species, ranging in length from a meter (3 feet) to 20 meters or more (65 feet). They had huge eyes, exceeding the size of pie plate in some of the larger species. That's a full-scale model of a Shonisaurus popularis in the picture above (the fat one is Geotripper himself, providing scale), the species found at Berlin-Ichthyosaur.
The bones of the ichthyosaurs were first noted by the miners, who used the massive vertebrae as doorstops and dinner plates. The site was excavated by paleontologists in the 1950s and 60s, who discovered more than three dozen more or less complete specimens. Nine or ten specimens were left in place for public viewing, and a structure was built over the site.
The bones don't differ overmuch in color from the surrounding rock, but the shapes are fairly obvious. The parallel bones above are ribs. Below are a number of vertebrae.
The skulls were the most delicate part of the skeleton, and were often crushed during preservation. Some portions of a skull are present in the photo below. Few teeth were found at the site.

One of the mysteries is why so many of the ichthyosaurs ended up dead in this one place. Numerous ideas have been suggested, including strandings, volcanic eruptions, spawning behaviour and others, but the favored explanation of the moment based on available evidence is that they died from mass poisoning, much as marine animals are killed today by red tides (toxic microorganisms). For more information on the topic, check out vignette 14 in Geology Underfoot in Central Nevada, by Orndorff, Wieder and Filkorn.
After our excellent tour by ranger Robin Riggs, we hit the road, and after a few hours we passed a welcome sign, the one that said we were back in California. Our beautiful home mountains, the Sierra Nevada, filled the horizon.
 Highway 120 is a very straight road in this part of the country!
Lest the students get lazy, we still had a few classes to go! We stopped in at Mono Lake County Park to sit in the grass under the Cottonwood trees. Mono Lake is an interior drainage lake; water flows in, but doesn't flow out. During the ice ages, glacial meltwater filled the basin, forming a lake 600 feet deeper that overflowed into adjacent basins, with water ultimately reaching Death Valley. In recent times the lake was 45 feet deeper than it is today, but in 1940, Los Angeles started diverting water from the incoming streams, and the lake started drying up.
 The spot we were walking on (below) was underwater half a century ago...
The lake is a critical stop for millions of migratory birds, as it has plentiful food in the form of fairy shrimp and brine flies. The birds need the nourishment to allow them to complete their long journeys. The conflict of human use and ecosystem preservation has dominated the politics of the region for decades. Recent agreements may stabilize the situation...maybe.
The mountains on the skyline are the Mono Craters, a series of rhyolite plug domes that have all erupted within the last 35,000 years or so. The last eruptions were only a few centuries ago. That makes this 9,000 foot ridge the youngest mountain range in the country.
Freshwater springs in the lake caused the formation of tufa towers, masses of calcium carbonate that stand like frozen sentries in the water.
After a quick lunch at the Whoa Nellie Deli, we headed over Tioga Pass and passed through Tuolumne Meadows in Yosemite National Park. By now, even the instructors wanted to go home, despite the incredible scenery. We will go see this stuff on a day trip later! Meanwhile we stopped for a wrap-up lecture and group photo at Olmsted Point. Half Dome loomed in the distance...
I snapped a quick picture of Mt. Conness and Tenaya Lake, and we got in the vans for the final hundred mile drive to Modesto.
We got in about 6 o'clock, and there were many happy shouts of reunions with loved ones. There was also a huge mess, but most of the students were cool enough to stay and help clean up. I love these folks! We were home. Mrs. Geotripper and I headed to the house said hi to our animals and managed to hang around the house for ten days before we got restless and hit the road again.
 As promised, here is the bunny. Mrs. Geotripper caught it in the early morning at Berlin-Ichthyosaur.
 It didn't fully cooperate in the careful posing category...
And that is the end of our Convergence of Wonders! I hope you enjoyed traveling with us!

3 comments:

Anonymous said...

Sure we did. Thanks a lot!

Gaelyn said...

This has been a great trip. I'm sure you'll have more to share about it.

Charles said...

Really enjoyed traveling along with you from my armchair. Hope to meet you some day, maybe on one of your trips. Thanks again for a great series of posts.